Silver salts and other photosensitive materials are used as a recording material that uses laser and other forms of light beams of high energy density. A thermal recording material is also used as such material. The recording layer of the thermal recording material has high optical density.
When it absorbs a light beam of high energy density, the local temperature increases causing thermal deformation such as melting, evaporation or aggregation to remove the irradiated area, whereupon a difference in optical density from the non-irradiated area is produced to achieve the recording of information. This thermal recording material has the following advantages: Photographic processing such as development or fixation is generally unnecessary; processing in a dark room is unnecessary since no information is recorded by ordinary indoor light; a high-contrast image is produced; additional recording (add-on recording) of information is possible.
In most cases, information is recorded on the thermal recording material by converting it to electrical signals in time sequence and scanning the recording material with a laser beam modulated according to the signals. One advantage of this recording mode is that a recorded image can be obtained on a real-time basis.
The recording layer of the thermal recording material may generally be made of cheap materials such as metal, dye and plastic. Thermal recording materials are described in, say, M. L. Levene et al., proceedings of 11th "Electron, Ion and Laser Beam Technology" Symposium, 1969; "Electronics", Mar. 18, 1968, p. 50; D. Maydan, "The Bell System Technical Journal", 50, 1971, p. 1761; and C. O. Carlson, "Science", 154, 1966, p. 1550. Thermal recording materials wherein the recording layer is made of metals comprise a thin film of Bi, Sn, In, etc. on a base, have desirable properties for thermal recording such as production of a high-resolution and high-contrast image. However, many recording materials using thin metal films reflect at least 50% of the laser beam and fail to use its energy effectively. Therefore, they require light of great energy for recording, and in order to record by high-speed scanning, a powerful laser beam source is necessary. This requires the use of large-scale expensive recording equipment. Several high-sensitivity recording materials have been studied. One example which consists of three layers of Se, Bi and Ge is described in U.S. Pat. No. 3,560,994. The recording material disclosed in this patent has a very thin Ge film that is formed on thin Se and Bi films to reduce their light reflectance. But the addition of Se is not desired since it presents pollution hazards. In addition, the quality of the image recorded by this material is not satisfactory.
Japanese Patent Application (OPI) No. 74632/76 (the symbol OPI as used herein means an unexamined published Japanese patent application) describes a recording material wherein an anti-reflection layer that absorbs light in the range of the wavelength of the laser beam used for recording is formed on a metal layer. However, it is very difficult to eliminate light reflection entirely by an anti-reflection layer. Even if it is possible to completely eliminate light reflection, a powerful laser beam source is still necessary for producing thermal deformations such as fusion, evaporation and aggregation by exposure to a laser beam. Therefore, a recording material of even higher sensitivity has been desired.